The present invention relates to a signal processor suitable for the processing of a read back waveform read from a recording medium such as for example an optical disc and a magnetic disc.
Removable, high-density optical discs such as CD-R/W (Compact Disc Re-Writable) and DVD (Digital Versatile Disc) have been utilized extensively in recent years, and their recording density has become higher and higher from year to year. On the other hand, in the field of magnetic disc technology, perpendicular magnetic recording has lately attracted attention, and it has been reported that an areal recording density as high as 100 Gbit/(inch)2 is realized (NIKKEI ELECTRONICS, 25 Sep. 2000, No. 779, pp. 204-211).
With a view to regenerating information high-density recorded on a recording medium without error, to date various signal processing methods have been examined. Such methods include PRML (Partial Response Maximum Likelihood), DFE (Decision Feedback Equalizer), TCPR (Trellis Coding Partial Response) and so forth, and for example these methods have been employed in signal processing LSIs for hard disk apparatus.
PRML employs a partial response (PR) method and the Viterbi decoding technique which is a maximum likelihood (ML) decoding technique. The partial response method is a signal processing method capable of performing data regeneration by positively making utilization of inter symbol interferences, i.e. interference between adjacent data or interference between read back waveforms. On the other hand, the Viterbi decoding technique, which is also called a maximum likelihood data series estimation method, is a method capable of regenerating a most reliable data series in time series by making use of previous data.
Conventionally, signal processors having a partial response characteristic which is represented in the form of PR (a, b, b, a) which is a tertiary transfer function characteristic, have been used. More specifically, PR (3, 4, 4, 3)-characteristic signal processors have been used in the past. However, this PR (3, 4, 4, 3) characteristic cannot be said to provide matching with the frequency characteristic of a read back waveform read from a recording medium.